diff --git a/xarray/coding/cftime_offsets.py b/xarray/coding/cftime_offsets.py
index 510e9dafad8..d6256e7acb1 100644
--- a/xarray/coding/cftime_offsets.py
+++ b/xarray/coding/cftime_offsets.py
@@ -289,20 +289,18 @@ def _shift_month(date, months, day_option: DayOption = "start"):
     _ = attempt_import("cftime")
 
     has_year_zero = date.has_year_zero
-    delta_year = (date.month + months) // 12
+    year = date.year + (date.month + months) // 12
     month = (date.month + months) % 12
 
     if month == 0:
         month = 12
-        delta_year = delta_year - 1
+        year -= 1
 
     if not has_year_zero:
-        if date.year < 0 and date.year + delta_year >= 0:
-            delta_year = delta_year + 1
-        elif date.year > 0 and date.year + delta_year <= 0:
-            delta_year = delta_year - 1
-
-    year = date.year + delta_year
+        if date.year < 0 <= year:
+            year += 1
+        elif year <= 0 < date.year:
+            year -= 1
 
     # Silence warnings associated with generating dates with years < 1.
     with warnings.catch_warnings():
diff --git a/xarray/plot/utils.py b/xarray/plot/utils.py
index a35128cadb6..dd47df703b5 100644
--- a/xarray/plot/utils.py
+++ b/xarray/plot/utils.py
@@ -248,9 +248,7 @@ def _determine_cmap_params(
             isinstance(levels, Iterable) and levels[0] * levels[-1] < 0
         )
         # kwargs not specific about divergent or not: infer defaults from data
-        divergent = (
-            ((vmin < 0) and (vmax > 0)) or not center_is_none or levels_are_divergent
-        )
+        divergent = (vmin < 0 < vmax) or not center_is_none or levels_are_divergent
     else:
         divergent = False